Heat exchange reactors of the double tube type are well known in the chemical field. They are especially useful when indirect heat exchange is required for providing or removing heat to or from a specific reaction.
A double tube device in its simplest form consists of an inner tube placed in an outer tube thus creating an annular volume in the space between the tubes. The placement of the inner tube inside the outer tube is very important for the function of the double tube. In many cases the best function is achieved by centring the inner tube inside the outer tube, but in other cases an asymmetrical placement of the inner tube is most effective. In all cases spacers are used to obtain the proper placement of the two tubes relative to each other. The function of the spacers is to fix the placement of the inner tube on the transverse cross section relative to the outer tube, while allowing for freedom of movement between the tubes in the longitudinal direction.
Double tube devices can have several uses in chemical reactors. One such use is in a double tube reactor in which a heat transfer fluid is transported in the annular volume of the double heat transfer tube, the heat transfer fluid serving to provide or obtain heat to or from a chemical reaction occurring outside the outer tube and/or inside the inner tube. Heat transport conditions to or from the heat transfer fluid transported in the annular volume are often not uniform along the perimeter of the outer heat transfer tube or even in some special cases of the inner heat transfer tube. Various heat transfer devices aimed at improving the heat transfer of the heat transfer fluid are known in the art.
The double tube reactor has one or more double heat transfer tubes. Typically catalyst is placed inside the inner tube. The double tube reactor can, however, also be used in a configuration with the double heat transfer tubes placed in a catalytic bed. Inside the inner tube could be fluid, catalyst or a void. The inner tube could also be substituted by a rod. Each double tube is therefore in this configuration surrounded by catalyst particles which can catalyse an exothermic or an endothermic reaction.
In the case where an exothermic chemical reaction occurs in the catalytic bed outside the double heat transfer tube, the heat generated results in external heating of the outer heat transfer tube.
Transfer of the generated heat to the heat transfer fluid in the annular volume can sometimes be problematic due to uneven heating of the outer heat transfer tube resulting in only some sections around the perimeter of the outer tube experiencing external heating. The heat transfer fluid flowing in the annular volume has a straight flow pattern and uneven heating of the outer heat transfer tube causes higher temperatures of the heat transfer fluid in some sections.
In the case where an endothermic chemical reaction occurs outside the double heat transfer tube, the heat required to enable the reaction to occur is provided by hot heat transfer fluid in the annular volume. When a double heat transfer tube is used together with other double heat transfer tubes higher temperatures are experienced in areas, where the distance to the nearest hot double tube is short. Where there is a longer distance between the double heat transfer tubes lower temperatures are experienced. This non-uniform gas temperature distribution causes uneven heating of the catalyst particles and this has an undesirable effect on the chemical reactions taking place in the reactor. The non-uniform temperature distribution in the catalytic bed results also in a non-uniform temperature distribution of the heat transfer fluid, when the heat transfer fluid flowing in the annular volume has a straight flow pattern.
It is an objective of this invention to provide a heat exchange process using a heat transfer medium having a helical flow path for indirect heat transfer to or from a fluid or a solid medium.
It is also an objective of the invention to provide a heat exchange reactor of the double tube type for use in the above process using a heat transfer medium for indirect heat transfer to or from a fluid or a solid medium surrounding the tubes.